A critical inspection report into SEND support in Derby found that families were being left "exasperated" by education, health and social care services' failures to identify support needed.
This included parents having to chase up information, forced to endure long delays and having to resort to paying privately for assessments.
"Many parents describe their exasperation about inconsistent and delayed approaches to the identification of children's SEND across education, health and social care services," states a letter to the city's clinical commissioning group and Derby City Council from the two inspectorates that carried out the visit, Ofsted and the Care Quality Commission (CQC).
"Parents often find themselves needing to repeatedly pursue professionals to follow up referrals and obtain feedback.
"A large proportion of parents described an ‘unfair' system where some access private assessments to get quicker results because of prolonged delays, while others are not able to do this."
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In addition, too many children are being incorrectly diagnosed as having a moderate learning difficulty (MLD) by health, social care and education services in Derby. This is leading to them being wrongly placed in specialist provision, inspectors found.
"Children and young people with SEND do not always receive accurate identification of their needs from the education, health and social care service," adds the inspectorates' letter.
"For example, a disproportionally large proportion of children and young people with SEND are identified as having a primary need of moderate learning difficulty (MLD).
"Leaders of the local area have identified that MLD identification may be ambiguous and is contributing to a significant proportion of children and young people being incorrectly placed in specialist provision."
During their visit in June inspectors found that frequent changes of council leadership over a number of years are a factor in the SEND failures, despite efforts to improve support over the last three years.
"These changes led to delays in leaders implementing the reforms effectively. Some initiatives were inconsistently applied and poorly co-ordinated.
"Despite a more proactive and determined approach by leaders over the last three years, too much time has passed before the necessary focus has been given to children and young people with SEND," says the inspectorates' letter.
Ofsted and the CQC have asked Derby's council and clinical commissioning group to provide a written statement on how they intend to improve support for SEND children.
Despite the concerns inspectors did note that the identification of support needed for early years children was good, and praised the co-location of health visiting and children's centre services in achieving this.
Evonne Williams, Derby City Council's cabinet member for children and young people, said: "Like most local areas, since the 2014 SEND reforms, we have struggled to keep pace with a significant increase in demand for assessments and resources for children with SEND compounded by the lack of sufficient government funding for these vulnerable children.
"This is an issue not just in Derby but across the country with around 80 per cent of areas inspected in the last 12 months also being required like us to complete a written statement of action.
"The local area will work hard to bring about the changes required."
Dr Steve Lloyd, medical director for NHS Derby and Derbyshire Clinical Commissioning Group, said: "Since Derbyshire's four CCGs became one in April this year it has meant the NHS is able to work much more closely and efficiently with local authority partners in the city.
"Some positive improvements have already been made, as highlighted by the inspectors, and we should be able to see the results of these and build on them with the further extensive work we have planned, which will be fully outlined in the joint action statement being submitted later this year."